This invention relates to automotive radio receivers and, more particularly, to improvements in the same.
Radios designed to mount in the dashboard of an automobile are commonplace. Because the radios are mounted in a limited space, they must be highly compact. Further, due to their mobile nature, such radios must have stringent circuit performance in order to handle the variable signal conditions they will encounter. Moreover, the automotive radio industry is highly competitive and the market place demands a reliable yet inexpensive product. The conflicting requirements of performance and size versus cost have forced the manufacturer to make serious tradeoffs. His ultimate design, invariably, involves numerous sacrifices.
In addition, altering an existing radio design to provide different or additional features has proved difficult. Rather than add FM circuitry to an existing AM radio design, manufacturers have had to redesign the entire radio to be AM/FM compatible. Modification of an existing radio designed for operation in the United States to the European system has similarly proved difficult.
The most troublesome part of a conventional car radio is the mechanical tuner. Commonly, such tuners employ slug tuned coils. A mechanical linkage transfers rotational actuation of the tuning knob to a lateral translation of cores within the slug tuned coils, and also provides approximate indication of tuning frequency. Such tuners are quite bulky and, as they are mechanical, have reliability problems. These problems are multiplied when push button type programmed tuning is desired. In addition automotive radios have been clumsy to operate. Proper tuning of all radios is critical, and, in a moving environment such tuning is difficult. To overcome these problems mechanical "automatic search" systems have been developed. These systems have proved to be bulky, expensive, and unreliable.
Due to advances in solid state technology, it is becoming increasingly more feasible to replace mechanical systems with their more reliable electronic counterparts. Advances such as large scale integration of active electronic devices in extremely compact integrated circuit form allow designers options not available heretofore. Further, "all electronic" systems allow modular "plug in" type designs, rendering a more easily serviceable and alterable product.